import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Point p1 = new Point();
        Point p2 = new Point();
        Scanner coordinate = new Scanner(System.in);
        while(coordinate.hasNextInt()){
            double x1 = coordinate.nextDouble();
            double y1 = coordinate.nextDouble();
            double x2 = coordinate.nextDouble();
            double y2 = coordinate.nextDouble();
            p1.setX(x1);
            p1.setY(y1);
            p2.setX(x2);
            p2.setY(y2);
            double x = p1.getX() - p2.getX();
            double y = p1.getY() - p2.getY();
            double len = Math.sqrt(x*x + y*y);
            System.out.printf("%.2f",len);
        }
    }
}
